1. Field of the Invention
The present invention relates to a method of manufacturing a semiconductor device, such as a method of forming a conductive film such as a wiring layer, a method of connecting wiring layers to each other, and a method of connecting leads to an element region formed on a semiconductor substrate.
2. Description of the Related Art
Forming a wiring layer on a semiconductor substrate, connecting wiring layers to each other on a semiconductor substrate, connecting an element region of a semiconductor substrate to another circuit, or connecting multilayered wirings to each other on a circuit substrate on which a plurality of semiconductor chips and the like are mounted is one of important steps in manufacturing a semiconductor device. More specifically, when a compact semiconductor device having a high integration density is developed, multilayered wirings must be formed on a circuit substrate, and the multilayered wirings must be efficiently connected to each other to form a highly accurate semiconductor substrate.
A conventional method of connecting multilayered wirings to each other on a circuit substrate on which a plurality of semiconductor chips are mounted will be described below with reference to FIG. 1. For example, a first wiring layer 2 having a desired pattern is formed on a silicon semiconductor substrate 1. The first wiring layer 2 has a Ti/Cu/Ti multilayered structure consisting of two Ti layers each having a thickness of about 600 .ANG. and a Cu layer having a thickness of about 3 .mu.m and interposed between the two Ti layers. The first wiring layer 2 is formed by vacuum deposition or sputtering. Subsequently, for example, a polyimide solution is coated on the entire surface of the semiconductor substrate 1 and dried to form a polyimide insulating film 3. A contact hole 31 is formed in the polyimide insulating interlayer 3 by using a photolithographic technique, and the polyimide insulating interlayer 3 serving as an insulating interlayer is sintered. A second wiring layer 4 consisting of Ti/Cu/Ti or Al is formed by the same steps as those of the first wiring layer. At this time, the second wiring layer 4 is also formed in the contact hole 31 so as to electrically connect the first wiring layer to the second wiring layer. The above steps are repeated to connect other multilayered wiring layers to each other. Note that reference numeral 5 denotes an insulating film.
FIGS. 2A to 2E are sectional views showing the steps in manufacturing a conventional bump electrode. In order to connect an external circuit to an integrated circuit formed in an element region of the semiconductor substrate 1, a connection pad electrode 6 formed in a non-element region of the peripheral portion of the semiconductor substrate and electrically connected to the integrated circuit is formed. A bump (projection) electrode 10 may be formed on the pad electrode 6 to connect the pad electrode to a lead connected to the external circuit. The bump electrode 10 has been conventionally formed by gold-electroplating. More specifically, as shown in FIG. 2A, a plurality of Al pad electrodes 6 are formed by sputtering in the non-element region of the peripheral portion of the silicon semiconductor substrate 1. Each of the pad electrodes 6 is electrically connected to a semiconductor element such as an integrated circuit formed on the semiconductor substrate 1. An insulating protective film 7 consisting of SiO.sub.2 is formed on the entire surface of the semiconductor substrate 1. Openings 7a are formed in regions of the insulating protective film 7 corresponding to positions at which the pad electrodes 6 are formed. As shown in FIG. 2B, one or more conductive films 8 required for electroplating are deposited on the entire surface of the resultant structure to cover the exposed pads 6 and the protective film 7. As shown in FIG. 2C, a photoresist 9 having a thickness of about 20 .mu.m is coated on the semiconductor substrate 1, and the photoresist 9 is exposed and developed to form openings 9a in the photoresist 9 above only the pad electrodes 6 on which the bump electrodes 10 are to be formed. As shown in FIG. 2D, the conductive film 8 is rendered conductive by conductive pins or the like to perform electroplating, thereby forming the gold bump electrodes 10 in the openings 9a. In this case, a region, such as the lower surface of the semiconductor substrate 1, which should not be gold-plated is covered with an insulator in advance. As shown in FIG. 2E, the unnecessary photoresist 9 is peeled, and the conductive film 8 except for the conductive film under the bump electrodes 10 is removed using the gold bump electrodes 10 as masks. The bump electrodes 10 are insulated from each other.
As described above, conventional wiring processing requires a photolithographic technique, an etching technique such as RIE, a step such as the step of removing a photoresist. Similarly, a complicate step is required when openings of an insulating interlayer required for electrically connecting upper and lower wiring layers to each other are formed. In addition, when a bump electrode is to be formed by electroplating, the step of forming a film by sputtering, the lithographic step of forming a plating mask using a photoresist, the electroplating step of forming a bump electrode, and the like are required such that the complicate steps must be performed. Therefore, these steps are added to the final steps of a wafer process, a production yield may be decreased, and reliability may be degraded.
In order to form fine metal particles by a material to be melted, an inert gas must be fed into an evaporation chamber in which a crucible is arranged, and the evaporated material must be cooled. At this time, when the flow velocity of the fed inert gas is high, a stream, i.e., smoke of fine particles which rises upwardly from the crucible is fluctuated. Fine particles cooled by the inert gas are moved upwardly by heat convection. The above fluctuation of the stream of fine particles occurs because the flow velocity of the inert gas is higher than that of the stream of fine particles moved upwardly by the heat convection. Once the fluctuation occurs, fine particles which do not enter the suction port of a feed pipe remain in the evaporation chamber. Such fine particles are coagulated with fine particles which are newly produced in the evaporation chamber, thereby producing large size fine particles. A fine particle film is formed to contain the large size fine particles, and the adhesion strength between the fine particle film and a substrate is considerably degraded.